Whether tiles may be fixed to a gypsum-based substrate depends not only on science but on the country in which you happen to be working.

British and American guidance, for example, have taken noticeably different approaches. Both recognise the same underlying reality. Yet they choose to manage it differently.

This concerns all calcium sulphate based substrates: gypsum plaster, bonding coats, anhydrite and alpha-hemihydrate screeds, Gyvlon and similar systems.

Gypsum contains calcium sulphate. Most tile adhesives are cementitious and contain reactive calcium aluminates. When these materials come into contact in the presence of moisture, they can react to form ettringite, or calcium sulfoaluminate: tiny white or yellow crystals that develop at the interface between the adhesive and the substrate. Excessive ettringite formation can weaken the bond and lead to debonding.

There is a certain irony here. Gypsum is itself added to Portland cement during manufacture. Without it, cement would set far too quickly to be practical. The difference is one of proportion. Portland cement contains only about four to five per cent gypsum, carefully controlled to regulate setting. Increase that proportion sufficiently and the chemistry changes. What is beneficial in small quantities becomes destructive in large ones.

Gypsum is not only chemically hostile to cement; it is also mechanically weaker than many cementitious backgrounds. British Gypsum, for example, distinguishes carefully between backing plasters and finishing plasters and imposes different limitations depending on how the plaster system has been constructed.

Heavy porcelain, thick natural stone and large-format tiles demand more from the substrate than gypsum is always able to provide. In some situations the limiting factor is no longer the adhesive but the plaster itself, or even the interface between the plaster and the wall behind it.

This is where British and American practices have historically diverged.

I can understand why. A tiled wall may look perfectly sound for weeks, months or even years before problems begin to appear. By then the installer has gone, the customer has settled into the house and the connection between cause and effect has become blurred. Delayed failure creates the comforting illusion that the method was correct all along. That is why being cautious seem the right way to go.

The plaster must be fully dry, sound and properly prepared. Special primers or membranes are used to create a barrier between the gypsum and the adhesive. Weight limits are imposed on the finished tiling, and manufacturers distinguish carefully between different gypsum products and methods of construction. The aim is not to deny the chemistry, but to control its consequences.